This invention relates generally to inflatable restraint systems and, more particularly, to an apparatus and method for inflating an inflatable device such as an inflatable vehicle occupant restraint for use in such systems.
It is well known to protect a vehicle occupant using a cushion or bag, e.g., an "airbag cushion," that is inflated or expanded with gas such as when the vehicle encounters sudden deceleration, such as in a collision. In such systems, the airbag cushion is normally housed in an uninflated and folded condition to minimize space requirements. Upon actuation of the system, the cushion begins to be inflated, in a matter of no more than a few milliseconds, with gas produced or supplied by a device commonly referred to as "an inflator."
Many types of inflator devices have been disclosed in the art for the inflating of one or more inflatable restraint system airbag cushions. Prior art inflator devices include compressed stored gas inflators, pyrotechnic inflators and hybrid inflators. Unfortunately, each of these types of inflator devices has been subject to certain disadvantages such as greater than desired weight and space requirements, production of undesired or non-preferred combustion products in greater than desired amounts, and production or emission of gases at a greater than desired temperature, for example.
In view of these and other related or similar problems and shortcomings, a new type of inflator, called a "fluid fueled inflator," has been developed. Such inflators are the subject of commonly assigned Smith et al., U.S. Pat. No. 5,470,104, issued Nov. 28, 1995; Rink, U.S. Pat. No. 5,494,312, issued Feb. 27, 1996; and Rink et al., U.S. Pat. No. 5,531,473, issued Jul. 2, 1996, the disclosures of which are fully incorporated herein by reference.
Such inflator devices typically utilize a fuel material in the form of a fluid, e.g., in the form of a gas, liquid, finely divided solid, or one or more combinations thereof, in the formation of an inflation gas for an airbag. In one such inflator device, the fluid fuel material is burned to produce gas which contacts a quantity of stored pressurized gas to produce inflation gas for use in inflating a respective inflatable device.
While such an inflator can successfully overcome, at least in part, some of the problems commonly associated with the above-identified prior types of inflator devices, there is a continuing need and demand for further improvements in safety, simplicity, effectiveness, economy and reliability in the apparatus and techniques used for inflating an inflatable device such as an airbag cushion.
To that end, the above-identified Rink, U.S. Pat. No. 5,669,629 discloses a new type of inflator wherein a gas source material undergoes decomposition or dissociation to form products including at least one gaseous product used to inflate an inflatable device. As disclosed in Rink, U.S. Pat. No. 5,669,629, a pyrotechnic load-containing initiator device can be actuated to commence dissociation or decomposition of the gas source material.
Such an inflator can be helpful in one or more of the following respects: reduction or minimization of concerns regarding the handling of content materials; production of relatively low temperature, non-harmful inflation gases; reduction or minimization of size and space requirements and avoidance or minimization of the risks or dangers of the gas producing or forming materials undergoing degradation (thermal or otherwise) over time as the inflator awaits activation.
"Rise rate," i.e., the rate at which the gas output from an inflator increases pressure as measured when such gas output is directed into a closed volume, is a common vehicular airbag inflator performance parameter used in the design, selection and evaluation of an inflator for particular airbag restraint system installations. In general, the rise rate produced by each of the above-identified types or kinds of inflator devices is controlled, selected or otherwise predetermined by the area provided by or in the particular inflator device for inflation output flow.
While the rise rate produced or resulting from an inflator, such as described above and which inflator contains a gas source material which undergoes decomposition or dissociation to form products including at least one gaseous product used to inflate an inflatable device, can be controlled or selected based on the inflation output flow through area provided by the inflator, such reliance can in practice be problematic. For example, restrictions in the inflation output flow through area provided by an inflator can result in dramatic increases in pressure within the inflator upon the actuation thereof. As will be appreciated, proper inflator design will generally necessitate that the inflator design account for such pressure increases, such as by inflator fabrication using materials of higher strength or through the use of increased inflator wall thicknesses.
Further, the inflation output flow through areas of such inflators are commonly normally covered or obstructed such as by means of one or more burst discs or the like, until such time flow therethrough is actuated. Thus, inflators with increased inflation output flow through areas commonly require burst discs or the like of increased strength or thickness. As will be appreciated, such uses of materials of higher strength or of greater thickness generally have associated therewith increased costs.
In view of the above, there is a need and a demand for an apparatus and a method for inflating an inflatable device such as an inflatable vehicle occupant restraint for use in an inflatable restraint system which permits either or both the design and control of the rise rate resulting from an inflator device such as an inflator device which contains a gas source material which undergoes decomposition or dissociation to form products, including at least one gaseous product used to inflate an inflatable device, without altering the inflation output flow through area of the inflator device.
Further, there is a continuing need and demand for further improvements in safety, simplicity, effectiveness, economy and reliability in the apparatus and techniques used for inflating an inflatable device such as an airbag cushion. More specifically, there is a need and a demand for an inflator device which can provide at least some of the benefits provided by the inflator of the above-identified Rink, U.S. Pat. No. 5,669,629, wherein a gas source material undergoes decompositional or dissociative-type reaction to form products including at least one gaseous product used to inflate an inflatable device while permitting either or both the design and control of the rise rate resulting from such an inflator device without altering the inflation output flow through area of the inflator.